In rotating shaft arrangements used in, for example, gas turbine engines, components, such as bearing races, radial scoops and seal plates, rotate with the shaft. Other elements of the arrangement, or adjacent elements, may abut the attached components but remain stationary as the shaft and attached components rotate, or may rotate at a different speed or in the opposite direction. The relative movement between the abutting elements causes friction at the interface between the elements. To reduce friction and to extend the useful life of the elements, lubricant, such as oil or grease, as provided at the interface.
FIG. 1 illustrates one example of a shaft arrangement where oil is provided to such an interface. A shaft 10 rotates under the force of a power transmission mechanism (not shown). Among other elements, the shaft 10 may have a radial scoop 12, a bearing inner race 14 for bearings 16, such as roller, ball or tapered bearings or the like, and a seal plate 18 mounted thereon for rotation with the shaft 10. A carbon element 20 is disposed about the shaft 10 but does not rotate with the shaft 10. The carbon element 20 abuts the seal plate 18 on a surface opposite the inner race 14. Lubricant is provided to the interface between the seal plate 18 and the carbon element 20 via a machined oil passage 22 through the seal plate 18. Pressurized oil is provided at the radial scoop 12 and flows through a plurality of circumferentially spaced openings 24 to slots 26 in an inner surface of the radial scoop 12. The slots 26 are in fluid communication with slots 28 in an inner surface of the inner race 14 extending from the radial scoop 12 to the seal plate 18. Slots 30 on an inner surface of the seal plate 18 connect the slots 28 to the inner race 14 to provide oil to the machined oil passage 22 and, correspondingly, to the interface between the seal plate 18 and the carbon element 20.
The prior art arrangement provides lubrication to the interface, but opportunities exist for improving the presently known configurations. For example, high stresses may be experienced in the machined oil passages 22 in the seal plate 18. The high stresses are attributed at least in part to high rotor speeds that are manifested within the machined oil passages 22 and result from the overall machined hole length and manufacturing limitations in hole size and surface texture control. In addition, the number of slots 28 in the inner race 14 varies, and the slots 28 may not always have a one-to-one correspondence with the slots 30 and machined oil passages 22 of the seal plate 18. This can lead to an uneven distribution of oil across the interface, with oil-rich areas where the slots 28, 30 align and oil lean areas where the slots 28, 30 do not align.
In view of the foregoing, a need exists for an improved arrangement wherein stresses in the machined oil passages are reduced and distribution of lubricant across the interface between the seal plate and the adjacent element is more uniform.